1. Technical Field
This application relates to an all-solid-state battery system and a method of manufacturing the same.
2. Description of Related Art
Currently, among various batteries, lithium ion batteries have attracted attention from the viewpoint of obtaining high energy density. Among the lithium ion batteries, in particular, an all-solid-state battery in which a liquid electrolyte is replaced with a solid electrolyte has attracted attention. The reason for this is as follows. Unlike secondary batteries in which a liquid electrolyte is used, in the all-solid-state battery, the electrolyte is solid, and a battery is composed of only solid. Therefore, for example, the decomposition of a liquid electrolyte does not occur, and cycle characteristics and energy density are expected to be high. Examples of a negative electrode active material which is generally used in a lithium ion battery include a carbon negative electrode active material such as graphite, soft carbon, or hard carbon. Recently, instead of the carbon electrode, an alloy negative electrode active material having a higher capacity has been studied. Examples of the alloy negative electrode active material include silicon, tin, germanium, and aluminum. Among these, in particular, silicon particles have attracted attention from the viewpoint of obtaining high capacity.
It is known that a battery in which an alloy negative electrode active material is used as a negative electrode active material has lower cycle characteristics than a battery in which a carbon negative electrode active material or the like is used as a negative electrode active material. The reasons for this are, for example, as follows; alloy negative electrode active material particles are pulverized by expansion and shrinkage during charging and discharging; and the internal resistance of an all-solid-state battery increases due to the formation of voids between alloy negative electrode active material particles and other negative electrode active material layer materials.
Japanese Patent Application Publication No. 2014-086218 (JP 2014-086218 A) discloses an all-solid-state battery in which silicon particles are used as an alloy negative electrode active material. In this all-solid-state battery, by adjusting the volume change amount of the silicon particles during charging and discharging, the crushing of the silicon particles and the formation of voids between the silicon particles and other negative electrode active material layer materials are reduced, thereby suppressing an increase in the internal resistance of the all-solid-state battery.
Japanese Patent Application Publication No. 2014-041783 (JP 2014-041783 A) discloses an all-solid-state battery in which silicon particles are used as an alloy negative electrode active material. By charging this all-solid-state battery at a lower voltage than under normal conditions once during the initial charging and discharging, the silicon particles are activated, and the utilization ratio thereof is improved. Further, JP 2014-041783 A discloses a method of favorably joining the silicon particles and other negative electrode active material layer materials to each other.
The all-solid-state battery in which alloy negative electrode active material particles are used as a negative electrode active material has a problem of low cycle characteristics due to the following reasons: the alloy negative electrode active material particles are pulverized by expansion and shrinkage during charging and discharging; and voids are formed between the alloy negative electrode active material particles and other negative electrode active material layer materials.
Therefore, in order to solve the above-described problems, a method of improving cycle characteristics of an all-solid-state battery in which alloy negative electrode active material particles are used as a negative electrode active material, is required. Specifically, for example, as disclosed in JP 2014-086218 A, in a case where silicon particles are used as alloy negative electrode active material particles, a method of improving cycle characteristics by adjusting the volume change amount of the silicon particles to reduce the resistance may be considered.
However, even in a case where the volume change amount is adjusted as disclosed in JP 2014-086218 A, cycle characteristics deteriorate. This result may imply not only the crushing of the silicon particles during expansion and shrinkage but also the progress of some chemical deterioration.
Accordingly, a technique of further improving cycle characteristics is required.